/*
 * Copyright© 2000 - 2021 SuperMap Software Co.Ltd. All rights reserved.
 * This program are made available under the terms of the Apache License, Version 2.0
 * which accompanies this distribution and is available at http://www.apache.org/licenses/LICENSE-2.0.html.
 */
package com.supermap.gaf.utils;

import java.util.UUID;

/**
 * <p>
 * 此类主要是完成主键唯一值 此类使用单例的模式读取，兼容多线程读取的问题
 * </p>
 *
 * @author ${Author}
 * @version ${Version}
 * @date:2021/3/25
 * @since 1.0.0
 */
public class PrimaryKeyUtil {

    /**
     * <p>
     * 私有化构造函数。
     * </p>
     */
    private PrimaryKeyUtil() {
    }

    /**
     * 静态的私有变量
     */
    private volatile static PrimaryKeyUtil m_instance;

    /**
     * <p>
     * 单例获取工具对象
     * </p>
     *
     * @return
     * @since 1.0.0
     */
    public static PrimaryKeyUtil getInstance() {
        if (m_instance == null) {
            synchronized (PrimaryKeyUtil.class) {
                if (m_instance == null) {
                    m_instance = new PrimaryKeyUtil();
                }
            }
        }
        return m_instance;
    }

    /**
     * <p>
     * 生成主键的值，此方法需要保证表内唯一
     * </p>
     *
     * @return
     * @since 1.0.0
     */
    public String GetPrimaryKeyValue() {

        String value = UUID.randomUUID().toString(); // 获取UUID并转化为String对象
        value = value.replace("-", ""); // 因为UUID本身为32位只是生成时多了“-”，
        return shortUrl(value)[0];
    }

    public String[] shortUrl(String url) {
        // 可以自定义生成 MD5 加密字符传前的混合 KEY
        String key = "supermap";
        // 要使用生成 URL 的字符
        String[] chars = new String[]{"a", "b", "c", "d", "e", "f", "g", "h",
                "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t",
                "u", "v", "w", "x", "y", "z", "0", "1", "2", "3", "4", "5",
                "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H",
                "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",
                "U", "V", "W", "X", "Y", "Z"
        };
        // 对传入网址进行 MD5 加密
        String sMD5EncryptResult = (Encript.md5(key + url));
        String hex = sMD5EncryptResult;
        String[] resUrl = new String[4];
        //得到 4组短链接字符串
        for (int i = 0; i < 4; i++) {
            // 把加密字符按照 8 位一组 16 进制与 0x3FFFFFFF 进行位与运算
            String sTempSubString = hex.substring(i * 8, i * 8 + 8);
            // 这里需要使用 long 型来转换，因为 Inteper .parseInt() 只能处理 31 位 , 首位为符号位 , 如果不用 long ，则会越界
            long lHexLong = 0x3FFFFFFF & Long.parseLong(sTempSubString, 16);
            String outChars = "";
            //循环获得每组6位的字符串
            for (int j = 0; j < 6; j++) {
                // 把得到的值与 0x0000003D 进行位与运算，取得字符数组 chars 索引(具体需要看chars数组的长度   以防下标溢出，注意起点为0)
                long index = 0x0000003D & lHexLong;
                // 把取得的字符相加
                outChars += chars[(int) index];
                // 每次循环按位右移 5 位
                lHexLong = lHexLong >> 5;
            }
            // 把字符串存入对应索引的输出数组
            resUrl[i] = outChars;
        }
        return resUrl;
    }
}
